public class P15 {
	public static int size = 20;
	
	public static void main(String[] args) {
		System.out.println(sum(0, 0, 0));
	}

	public static long sum(int column, int row, long sum) {
		for (int i = row; i < size + 1; i++) {
			if (column == size - 1) {
				return sum + (size - row + 1);
			} else {
				sum = sum(column + 1, i, sum);
			}
		}
		return sum;
	}
}